1. Field of the Invention
The present invention relates to an electronic controlled suspension system using wheel speed thereinafter an ECS control system. More specifically the present invention relates to an ECS control system not using a G sensor and a steering angle sensor but using a control algorithm and an antilock brake system (ABS) wheel speed sensor in order to perform rough road detecting and roll control.
2. Detailed Description of the Related Arts
One example of known semi-active type suspension systems is an ECS system (10) as shown in FIG. 1, which controls the damping force of the shock absorber by the input of the G sensor (12), steering angle sensor (14), vehicle speed sensor (16), inhibitor switch (17), throttle position sensor (TPS) (18) and stop lamp switch (19). Data obtained from the G sensor (12), steering angle sensor (14), vehicle speed sensor (16), inhibitor switch (17), throttle position sensor (18) and stop lamp switch (19) are inputted, respectively, to the rough road detecting part (22), anti-roll detecting part (24), wheel speed response part (26), anti-shift detecting part (27), anti-squat detecting part (28) and anti-dive detecting part (29) of the ECS system (10).
Heretofore most of the semi-active type suspension systems were of a 2-step or 3-step damping force control type, but nowadays, the use of the continuously variable type damper is increasing.
Although the continuously variable type damper can improve ride comfort by using sky-hook control etc., it has a problem that it makes a system complicated and raises price due to the increased sensors. Also, the semi-active type suspension system has a defect that riders do not feel comfort when driving.
The conventional analysis of the signals from the wheel speed sensor indicates that the peak frequency of the frequency response of the pitch rate is identical with the wave-type peak frequency of the wheel speed sensor below 5 Hz, as shown in FIG. 2.
Meanwhile, improving the ride comfort means reducing the vibration of a vehicle, as shown in FIG. 3. For this purpose, it is necessary to make the damping force hard in low frequency including the resonance frequency of the body of a vehicle, and make the damping force soft in high frequency. Therefore, the main factor of improving the ride comfort is detecting the vibration of the body of a vehicle in the low frequency range.
A pitching develops between the wheel speed and the movement of a vehicle according to the road condition when the vehicle is driving at a constant speed V, as shown in FIG. 2. At this moment, the wheel speed sensor rotates according to the change of pitching. Therefore, the signal of the wheel speed changes with pitching.
Namely, the wheel angular velocity becomes .theta..sub.v +.theta..sub.p, or the wheel angular velocity is expressed by the following equation: EQU V.sub.p =K(.theta.v+.theta.p)
, wherein
K: constant
.theta..sub.v : angular velocity when the vehicle speed is V
.theta..sub.p : angular velocity due to the pitching
The ride comfort is improved by detecting the movement of a vehicle and changing the damping force by use of the wheel speed sensor, based on the above equation. FIG. 4 is a block diagram of the conventional ECS control system, in which the data measured by the wheel speed sensor is inputted to the suspension electronic control unit (ECU) (50) via antilock brake system (ABS) ECU (41). And a frequency sensing circuit (52) is mounted inside the suspension ECU (50). Also, several damping force actuators (43, 45, 47 & 49) and shock absorbers (42, 44, 46 & 48) are connected to the suspension ECU.
Meanwhile, FIG. 5 represents the result of the ride comfort control effect of the real-vehicle test, which shows that the vibration decreases around the resonance point of the vehicle body.
As mentioned above, in spite of the mounting of ABS, the conventional semi-active type suspension system has the disadvantage in that the ECS system is complicated due to the use of additional G sensors, steering angle sensors, wheel speed sensors, etc., and the cost is high due to the sensors performing the same functions.